Teleprotection is an essential requirement for operating and maintaining a reliable, robust, and safe electrical power grid. The current of a power signal is measured at a first location and transmitted over a communication channel to a second location. Simultaneously, the current of the power signal is measured at the second location and transmitted over a communication channel to the first location. Comparison of time-aligned observations of the power signal may reveal different measured values of the current at each location. This is usually indicative of a fault in the power grid, and action can be taken to remedy the fault.
The current is measured several times per cycle of the power, and therefore time-alignment is very important. There is inevitably some delay in communicating between the two locations, but TDM networks offer a very symmetric communication channel. Delays introduced by the communication channel in one direction are generally the same as delays introduced by the communication channel in the other direction. The delays are effectively the same in each direction, so time-alignment of observations is still possible.
Nowadays core networks are evolving to packet switched networks. However legacy systems still require TDM services. Circuit Emulation Services (CES) are used to provide TDM services, as are required by legacy teleprotection systems, over packet switched networks. The routers at the edge of the packet switched network provide CES, and the devices of the teleprotection system which measure the current of the power signal send their measured observations to the routers over T1/E1 lines. The routers use their CES to transmit the measured observations to each other as packet data. The observations are then converted back into TDM format and sent to the teleprotection devices over T1/E1 lines, where they are used in teleprotection analysis.
However packet networks are asymmetric, in that the delay introduced by the network in one direction is not necessarily the same as the delay introduced by the network in the other direction. Differences between the delays may arise for example because different paths are used in the directions, or because of differences in store-and-forward techniques along the paths. The asymmetry in communications makes time-alignment of the power observations difficult, and therefore teleprotection analysis more difficult.
A system and method which allowed improved time-alignment of observations even when transmitted over asymmetric communication networks would allow teleprotection systems to better use packet switched networks.